1. Technical Field
The present invention relates generally to a solid state storage system and a method for controlling the same, and more particularly to a solid state storage system for controlling a reserved area flexibly, and a method for controlling the same.
2. Related Art
Nonvolatile memories are widely used as storage memories for portable information devices. A recent trend is utilizing solid state drives (SSDs) using NAND flash memories in personal computers (PC), instead of conventional hard disk drives (HDD). Further, SSDs using NAND flash memories are commercially available, and are expected to make inroads into HDD markets.
However SSDs can be problematic as bad blocks may occur during the use of such SDDs. Bad blocks may be caused by process failure of flash memories, or may by degradation in characteristics of flash memory cells due to frequent operations. Such bad blocks are replaced with blocks of a reserved area in order not to refer to physical areas of the bad blocks. To accommodate the necessity for replacing bad blocks, a reserved area space is allocated. That is, additional physical areas are allocated and used only for the purpose of replacing the bad blocks.
For the efficient management of blocks, an address mapping is performed. The address mapping is to connect a logical address of a block provided from the external to an address of a physical area of a block practically stored. Since the reserved area is an area allocated only for the purpose of replacing a bad block, it is not associated with a normal data area. Hence, the reserved area is excluded from the address mapping. However, it is necessary to allocate an additional bad block management map for managing information on position of the bad block. The additional allocation of the bad block management map degrades the entire memory efficiency. Moreover, when the number of occurrence of bad blocks is small, the use efficiency of the already allocated extra reserved area is degraded.